Revelations: “the sky weeping tears for the ocean..”

Mass bleaching – a phenomenon caused by global warming-induced rises to sea surface temperatures – has occurred on the reef four times in recorded history.

Prof Terry Hughes, who led the surveys, said the length of time coral needed to recover – about 10 years for fast-growing types – raised serious concerns about the increasing frequency of mass bleaching events.

“The significance of bleaching this year is that it’s back to back, so there’s been zero time for recovery,” Hughes told the Guardian. “It’s too early yet to tell what the full death toll will be from this year’s bleaching, but clearly it will extend 500km south of last year’s bleaching.” Last year, in the worst-affected areas to the reef’s north, roughly two-thirds of shallow-water corals were lost.

Hughes has warned Australia now faces a closing window to save the reef by taking decisive action on climate change.